1. Field of the Invention
This invention is directed toward a boom unit used in a tree processor.
2. Description of the Related Art
Boom units for tree processors, such as delimbers, are known. The boom unit has a boom movably mounted through a tubular support, the support rotatably and pivotably mountable on a vehicle. The boom is movable through the support to first grip and to then lift and move a cut tree to be held by the support at its cut end. The boom is then moved relative to the support and the held tree to delimb it. The boom is normally rectangular in cross-section with a height greater than its width. The boom rests on a flat, bottom side in the tubular support, the bottom side horizontal. There are boom support means on the support, usually in the form of top, bottom, and side rollers at both ends of the support, between which the boom moves. The top and bottom rollers minimize up and down movement of the boom while the side rollers minimize sideways movement of the boom. Boom moving means, usually in the form of a chain and sprocket drive with the chain mounted on top of the boom, and the sprocket mounted on the support, move the boom forwardly and rearwardly through the support.
The mounting of the boom in the above manner however results in high maintenance of the unit. The boom, because of the nature of the work, is constantly being forced against the rollers with sideways forces and sudden up and down forces when a tree is gripped and lifted by the boom or when a tree is released by the boom. Each bottom roller is unequally stressed when the boom is forced against either side during use leading to rapid wear and replacement of the bottom rollers. In addition, the chain and sprocket drive used to move the boom through the support is constantly stressed due to lateral movement of the boom and the attached chain relative to the support and attached sprocket and also requires frequent maintenance and replacement.
In an effort to reduce maintenance, it is known to provide a boom unit having a boom with a square cross-section, the boom mounted through a tubular support and movable through the support in either direction. The support supports the boom with opposed corners of the boom on a vertical center line so that one corner of the boom is at the bottom center of the boom. Such a boom is shown in U.S. Pat. No. 3,735,786 issued May 29, 1973 to Rudy Vit. The support is constructed with four walls defining a tube with a square cross-section and positioned to support the boom with a boom corner at the bottom. Rollers are mounted in all four walls of the support at its front and rear ends to movably support the boom for movement through the support and to minimize movement of the boom both up and down and sideways in the support. The mounting the boom on a corner, rather than on a side, centers the boom on the two bottom rollers at the front and rear of the support. When the boom is extended relative to the support and picks up a tree, the load is transferred to the bottom, front rollers and the top, rear rollers of the support. Mounting the boom in the above manner, where it is cradled between the bottom rollers, equalizes the load between the bottom rollers and reduces maintenance compared to the maintenance required by booms with a rectangular cross-section mounted on a narrow side.
However, the arrangement of using a boom with a square cross-section, the boom mounted on a corner, still requires frequent maintenance. The system uses a relatively large number of rollers all of which require servicing. The front, top and rear, bottom rollers, while not load bearing to the same extent as the front, bottom and rear, top rollers, are unequally affected by sideways and up and down movements of the boom during use. Also, all the rollers are each mounted with a pin supported by bushings and roller bearings at each end. Replacement of any roller and/or the bearings is difficult. In addition, a drive means other than a chain and sprocket drive is required to move a boom mounted on a corner and the different drive means used is quite complicated.